1. Field of the Invention
The present invention relates to a printed circuit board, and particularly to a printed circuit board which has improved solder pads layout.
2. Description of Related Art
Conventional printed circuit boards each define a plurality of through holes. The through holes are provided for extension of leads of components. The components are connected with the printed circuit board with the leads soldered thereto. A solder pad area is provided around each through hole when layout. Circuit is not laid in the pad areas and the pad areas are commonly covered with solder. The components are attached to the printed circuit board by wave soldering or reflow soldering. The pad areas are for preventing short circuit between the components and the circuit around the components on the printed circuit board.
Bigger components with axial leads are typically inserted into the printed circuit board manually. This insertion process is unduly laborious and time-consuming and has a low efficiency. An improved method of inserting components to corresponding through holes of the printed circuit board by placement machines is provided. This operation can greatly increase the efficiency.
The axial leads of the components should be perpendicular to the printed circuit board. But the axial leads are often bent when the components are inserted into the through holes by machine. The bent angles are different according to different placement machine. FIGS. 5 to 8 show four kinds of commonly bent angles respectively. Through holes 10′ and 11′ of the printed circuit board provide a component (not shown) with two axial leads to extend therethrough. The through holes 10′ and 11′ are surrounded by solder pads 20′ and 21′, respectively. Numbers 30′ and 31′ indicate two axial leads of the components. Letters a1, a2, b1 and b2 respectively indicate the angles of that the axial lead 30′ and the axial lead 21′ away from the through hole 10′ and through hole 11′. The placement machine determines the values of a1, a2, b1 and b2. Usually, a1=a2=45 degrees, b1=b2=45 degrees. Commonly, only one of these bent angles will happen when one kind of placement machine is used to insert the components. When the axial lead of the component is out of the area of the soldering pad, it is prone to touch the circuit that surrounds the soldering pad. Thus a short circuit in the printed circuit board occurs and this causes damage to the printed circuit board.
An improved printed circuit board that overcomes the above-mentioned problems is desired.